1. Field of the Invention
The present invention relates to a method for producing a plastic lens having high hardness and excellent scratch resistance by polymerizing and casting a diethylene glycol bis(allyl carbonate) in a desired lens-forming mold.
2. Description of the Prior Art
Plastic lenses produced by polymerizing and casting diethylene glycol bis(allyl carbonate) by using organic peroxides having a decomposition temperature at selected half-life value for ten hours of not higher than 80.degree. C., particularly di-isopropyl peroxydicarbonate, as a polymerization initiator have been very important particularly as spectacle lenses, because plastic lenses have many characteristics not possessed by usual glass lenses. For example, they are light in weight and dyeable.
However, plastic lenses have great drawbacks in that they are readily scratched because of lower hardness than glass lenses. For obviating this drawback, plastic lenses having equal surface hardness and scratch resistance to glass lenses have been produced by applying a thermosetting resin, such as a silicone resin, a polyester resin, a melamine resin and the like or a polyfunctional monomer, such as allyl acrylate or allyl methacrylate on surfaces of a plastic lens obtained from diethylene glycol bis(allyl carbonate) and thermosetting said resin or monomer, and these lenses are commercially available.
Although these plastic lenses wherein a thermosetting resin and the like have been applied on the surfaces of the lens have highly improved surface hardness and scratch resistance, the excellent dyeability which is one of great characteristics of plastic lenses is lost. Furthermore, new drawbacks have been caused. For example, the steps for coating and curing the thermosetting resin are added and it is difficult uniformly to coat the thermosetting resin and the like on the surfaces of the lens, so that the precision of the surfaces of the lens is lowered and the production of lenses having complicated shapes becomes difficult. In addition, in plastic lenses, unpolymerized substances, such as diethylene glycol bis(allyl carbonate) remain in the lens different from glass lens, irrelative to the practice of the surface working and these remained substances make the uniform formation of reflection preventing film through vacuum evaporation difficult.